Liquid phase oxidation of cyclohexane



March 4,

Filed May 4, 1954 A. scT-TuELER ETAL 28255742 LIQUID PHASE OXIDATION OF CYCLOHEXANE 2 Shets-Shee t 1 7" .15 lg. .E

CYCEOREXAN A STORAGE 2 A A 1? I CONDENSERS a OXIDIZER gWATER 1.939%??? WATER 1 3\ WATER Q EXTRACTION i 2 I q A M CONDENSERS AlR 2 OXiDIZER ;WATER l g L fiii l fu WATER I WATER & P

EXTRACTION 9 I CONDENSERS W 3 OxTmzER WATER I 6 L BAWPEL,

A k WATER u 10 i 7 A PHASE OXIDATION sEPARATOR PRODUCTS DlSTlLLATION OF CYCLOHEXANE LOWER PHASE RECOVERY l3 2 J1 OXIDIZED INVENTORS PRODUCTS FREDERICK A. WOLFF ATTORNEY March 4, 1958 A; P. SCHUELER ETAL ,8

LIQUID PHASE OXIDATION OF CYCLOHEXANE 2 Sheets-Sheet 2 Filed May 4, 1954 MULTISTAGE WITH INTERSTAGE WATER EXTRACTION MULTI STAGE WITHOUT WATER T. A B

u w mm n n C C o M 5 T T oo 00 ow on ow CYC LOH EXAN-E CONVERSION,

INVENTORS FREDERICK A. WOLFF ATTORNEY LIQUID PHASE OXIDATIGN F CYCLGHEXANE Arnold P. Schueler and Frederick A. Wold, Wilmington,

DEL, assignors to E. i. du Pont de Nemours and Company, Wilmington, Del, a corporation of Delaware Application May 4, 1954, Serial No. 427,448

Claims. (Cl. 260586) This invention relates to the oxidation of liquid hydrocarbons with gaseous oxygen and more particularly to oxidation of cyclohexane or cyclohexane-containing petroleum fractions.

-It is now well known that oxidation of cyclohexane to partial oxidation products constitutes an important step in the manufacture of nylon intermediates, e. g. adipic acid. The process of oxidizing cyclohexane in the liquid phase to cyclohexanol and cyclohexanone at low conversions and high yields was disclosed several years ago (cf. the Loder Patents U. S. 2,223,493; 2,223,494; and 2,321,551). In general, this process, when carried out on a laboratory scale, gave cyclohexanol-cyclohexanone yields of about 85 to 95% when the percentage of cyclhexane molecules oxidized was less than 5%. When the percentage of cyclohexane molecules oxidized was i from about 5% to about 12%, the yield of cyclohexanolcyclohexanone was about 65% to 85%. In practical operations it is feasible to sacrifice yield at any given conversion level in order to have a process which permits continued operation for many months or years, without shutdowns for removal of accumulated by-products.

In the manufacture of adipic acid from cyclohexane it was at one time considered that best results could be obtained by oxidizing cyclohexane to cyclohexanol and cyclohexanone in high yield and low conversion (U. S. 2,223,494) followed by separation of these intermediates, thereafter converting the cyclohexanol to cyclohexanone, and oxidizing the latter to adipic acid with air in a separate operation. More recently it has been disclosed (U. S. 2,439,513) that far better overall results are obtained by oxidizing mixed primary oxidation products (obtained from cyclohexane) to adipic acid by means of a nitric acid oxidation process. This made the obtaining of maximum yields of cyclohexanol and cyclohexanone, (the yield of cyclohexanol-cyclohexanone is maximum at low conversions) less desirable an objective than the obtaining of maximum yields of the mixed oxidation product which in the subsequent steps would be convertible to adipic acid. The present invention is concerned with a process for oxidizing cyclohexane to cyclohexanol and cyclohexanone, and to other products which are of value as adipic acid intermediates (as well as to still other products which are also of great value, as disclosed hereinafter); a purpose of the invention is to accomplish this desirable result by means of a process which is suitable for large scale production, i. e. which does not necessitate conversions below about 5%, and which can be operated for an unlimited period of time without any need for purging of excessive amounts of valuable ingredients, which would otherwise accumulate and preclude continued operation of the process.

It is well recognized, in commercial operations of the type just described, that best results are obtained by removing water from the oxidation vessel as soon as it is formed, and this is accomplished in large scale operations by performing the oxidation in a series of reactors, each of which is equipped with a condenser for 2,825,742 iatented Mar. 4, 1958 continuously separating water from the ofi gas stream, while simultaneously condensing cyclohexane from the same stream and returning the latter to one or more of the oxidation vessels. This arrangement of equipment is illustrated in U. S. Patent 2,557,281, which issued on June 19, 1951. If water is not continuously removed, substances which serve as initiators and accelerate the desired reactions are partially removed from the reaction zone, and the reaction takes a somewhat undesirable course, yielding larger quantities of acids than would otherwise be formed at the same conversion level. It is also recognized in this art that the latter efl'ect should be avoided even when adipic acid is the product which is to be sought in a subsequent nitric acid oxidation step, because adipic acid formation is never selective when it is produced directly by the air oxidation route. In fact, the formation of adipic acid in one-step liquid phase oxidation of cyclohexane (Loder U. S. 2,223,493) occurs at mediocre yields (e. g. 35 to 40%), the preferred techniques for oxidizing cyclohexane to primary products, followed by oxidation of the latter to adipic acid by means of nitric acid, as hereinabove mentioned, give yields which are about twice as high as in this previously known one step process.

A recently disclosed modification of the one step process for making adipic acid from cyclohexane has been to add water to the oxidation vessel, and to withdraw aqueous adipic acid periodically therefrom (German Patent 854,505). The latter process evidently facilitates removal of adipic acid from the oxidizer, but it involves carrying out the oxidation in an aqueous system, which is undesirable, as explained above. Moreover, facility in removing adipic acid can also be achieved by injecting water into the effiuent from the oxidizers, when water is not permitted to accumulate in the oxidation mixture, .as disclosed in the above-mentioned U. S. Patent 2,557,281, if the amount of adipic acid formed is not large.

It is essential in the practice of the present invention, as in the process of U. S. 2,557,281, to provide a means for removal of water from the reaction zone, since water, which is produced as one of the products of the oxidation reaction, affects the oxidation reaction adversely. The above-described method for removal of water, namely by having the oxidizer (or each of them if there is more than one) equipped with a reflux condenser and a device for withdrawal of water layer from the condensate produced by the said condenser, is entirely suitable in the process to be described below.

It has been discovered according to this invention that valuable advantages result, in the liquid phase oxidation of cyclohexane to such primary products as cyclohexanol, cyclohexanone, and other sources of adipic acid, under substantially anhydrous conditions, i. e., with removal of water azeotropically substantially as fast as formed, it at successive stages during the course of the oxidation the liquid oxidation mixture is extracted with water. In this way not only is the water content of the oxidation mixture held at a low or minimum level, which is advantageous as has been explained, but also the yield of products which are convertible to adipic acid becomes virtually independent of the percentage conversion of cyclohexane, over a relatively wide range of conversion.

The oxidation of cyclohexane is carried out, according to this invention, in the liquid phase at a temperature between and 200 C. under 50 to 500 pounds per square inch pressure with the oxygen absorption limited so that about 3% to 20%, preferably about 10% to 20%, of the hydrocarbon present is oxidized, with water extraction at successive stages, as just described. Another method of practicing the invention is to operate a single oxidizer while Withdrawing a side stream 3 1 therefrom, continuously extracting the sidestream ..with water and conducting the. extracted stream back to the oxidizer. The water layer can be sent to a toppmg still l a'nd' the distillate recycled.

Such a side streamiif desired can beehined to' 50 3 100 C. to cause a second .zliquid phase to separate out.

Removal of the latter hasa beneficial effect on yield at"relatively high conversion levels within the operable 1 range. I

' Thus; the 'present invention 'provides a process for manufacturing partial oxidation products of cyclohexane, notably cyclohexanol' and cyclohexanone, by reacting 1Y1 cyclohexane in -the-liquid :iphase-with gaseous oxygen at a temperature between"'75-and=*200 C. (preferably 125 to 165 C.) under-O to500 "(preferably 50 to 250) w pounds per. square inch pressure, continuing the oxida- ;tion*un'til' fro'r'n"5% to 30%. of thehydrocarbon has become oxidized, while separating from the oxidation mixtile than cyclohexane, said portion being rich in cyclohexanol and cyclohexanoneln general, the yield'of "-"cyclohexanol-andcyclohex-anone in' this process on a -large scale is from" 65% to -85% based upon the quantity of cyclohexane-consumed, and the total yield of partialoxidation products which yield adipic acid'upon further oxidation, is' substa'ntially higher" than the yield of cyclohexanol-cyclohexanone. Moreover, the yield of adipic acid' precursors is "virtually independent of'conversion over therange of conversion mentioned.

desired; the-process of=this-invention"may becarried out in=theabsenee of an added catalyst. "However, '-it-has been found=that somewhat higher yields of cycle- 'hexanol and cyelohexanone areobtained if at-leasta small quantity'ofcatalyst is'employed. 'The quantity of catalyst may, indeed, be extremely minute, e. g. as little as 5 0.1 'partpenmillion of cobalt in the form of a hydrocarborpsoluble salt. -Othercatalysts which may be em- ==ployed-in placeof cobalt '(quantity, 0.1 to 1,000 parts 4 per million, preferably'about 0.5 to 50 parts per million) include hydrocarbon-soluble'compounds ofcop- =2: per," cerium; vanadium,- chromium; manganese; etc; The hydrocarbon-soluble compounds of cobalt,however, give i the best results.

The process of this invention may be carried out in -any suitable equipment, e. g., tubular reactors," tower reactors, or stirred autoclavesb Best'results' are obtained "a'vvhen' the oxidation vessel'which'is employed is'a stirred a-utoclave', or when the'process is operated in" a "contin- ='-'--uous manner, a' number of-such'stirred autoclaves in a 1 series? If desired; several" such series; can be: connected 'in 'par'allely-for exampleythere may be nineautoclavcs arranged so-that-there arethree trains, each containing three' autoclavesl' Each" of the autoclaves: should be equipped-with "a water-withdrawing means (condenser, with water draw-ofi) as stated above. When: water removal is accomplished azeotropically bymeans of a'con- -denser (generallyoperating at" the pressure of theoxi- 'dizer) in the. oif-gas line after each autoclave; .the recoveredhydrocarbon which is condensed along with thewater azeoti-opically shouldbe separated in a' decanter and can be piped to one of the oxidizers, or to the main hydrocarbon recoverystill'." The reaction mixture may be' passed through the autoclaves continuously, the efiiu- 'ent'frorn the. first passing to thesecondQand so 011.. "The efliueirt from the last autoclave is," in preferred: embodimentspconducted toa fractionating columnfor recovery cr'of the unus'ed"hydrocarboni' If desired this can ,be preiminarily c'hilled'to '50". 'l'00 'C. to cause formation of a secotid liquidphase t:admittingacidr the hydrocarbon azeotropic distillate boils for the .most part at tai'temperature very close to the boiling point .of cyclohexane, just below 81 C., and entirely within the range of 40 to 81 C. The main cyclohexane fraction," which of course contains a smaller percentage of benzene than 5 the percentage of benzene in the oxidation mixture, is

The final off-gas is V returned to the oxidation vessel. generally scrubbed with a high-boiling hydrocarbon or .-;passed. through a low temperature condenser for're'covery z. offurther amounts of cyclohexane. -.vantage1in the yield ofcyclohexanol'and cyclohexanone A remarkable ad- (amounting to several percent at a conversion'of' about z 15%) isobtained if the recovered cyclohexane from the decanters and/or from the main hydrocarbon recovery still is returnedto the first oxidizer,"rather'than 'to'the 5 ;second, or third, or subsequent oxidizer. The "reason forthis is that it resultsin a lower concentration .of'primaryxoxidation products in the first'oxidizers, i. e, the

avera'gez concentration-along the train is lowered if'the zjwmixture; isidiluted":with recycledhydrocarbon at th'e's'tart 0 :of thentrain, rather-than at the end thereof. Allof. the

recovered cyclohexane is preferably returned to the'first cOXiCliZBI for this reason.

A'mostneconomical method for workingup the'reaoz-tionaproducts contained in the oxidizer 'efiluent is the vso -called Wet KA process disclosed'in 'copendiu'g'U. S.

,wpatentapplication'S. N.390,634, filed 'onNovemb'er6, 1953; nowv Patent No. 2,703,331. According to the latter process the oxidizablefeed which is" conducted "to the nitric acid oxidizer for production of adipic acid is 40 an oil' distillate obtained by injecting Waterintb the efiluent from a liquid phase cyclohcxane oxidation vessel, separating hydrocarbon and aqueous phases from the .'-.result1ng mixture, removing steam distillable oilgtrom the:;said aqueous phase, adding said oil-to the hydrocarbon'phase, stripping substantially all of the hydrocarbon from the resulting mixture, and exhaustively steam disi-, tilling.the. resulting residue, whereby the said oil which is suitable for use as oxidizable feed to thenitriciacid .oxidizerdszobtained.

Whiletit is essential that the water :which is produced for; this 1 is that adipie -acid,-"and other solid products,

:icrystallize'aout whenthe-oxidation2mixture is cooled. :.Wateristhereforepreferably added to the oxidation mix- :rture after'it leaves the'oxidizer but'beforea the hydrocarvbon recovery, to prevent precipitation ofiadipicacid.

60.-Also. thepresence of 'wateris advantageous during the --..hydrocarbon recovery operations'because it.suppresses-dehydration of cyclohexanol 'and"cyclohexanone to such aspro'ducts as cyclohexylidene *cyclohexanone, cycloh'exyl .ethers, and 'cyclohexyl esters.

Figure '1 of the accompanying diagrammatic drawing illustrates one method; of' practicing the invention. Cyclohexane," from the-=-storage-vessel 1, ispumped into an 1 oxidation vessel-2; which' may be an autoclave equipped 7 -jected=toextraction "with'waterinthe' vessel 3'. LTI'he 1.extracfed' -hydrocarbon' phase is." conducted to the second oxidizer 4; -thence, to a second water extraction 5, and to *ta third oxidizer 6." '.'Each' "oxidizer. isequiPpedwithLcondenser-s, (e. g. refluxicondenseranda condenser-decanter "which-"p ermits' return ofhydrocarbon and withdrawal "of condensers 7, 8, and/or 9. The total oxidation products 10, can be treated directly by pumping both phases to a still for recovery of cyclohexane, or preferably the aqueous phase can be removed 11 and separately distilled for recovery of steam distillable oil 12. The latter can be united with the hydrocarbon phase in the product 10, and distilled 13 for recovery of cyclohexane. The latter is returned to the storage vessel 1. The residue, comprising all organic products 14 higher boiling than cyclohexane, is ready for conversion to adipic acid by nitric acid oxidation.

A noteworthy observation, which is of considerable interest from a theoretical and practical standpoint, is that the addition of cyclohexanol and cyclohexanone to e initial cyclohexane feed in substantial amounts does not produce a yield-lowering eiiect of the same order of magnitude as the yield-lowering effect which attends correspondingly increased conversion of cyclohexane to cyclohexanol and cyclohexanone. From this observation it can be deduced that probably some other ingredient or ingredients of the oxidized mixture, formed during the oxidation, adversely affects the yield of adipic acid precursors. The present invention provides a method for intermittently removing such ingredient or ingredients from the reaction mixture, during the course of the oxidation reaction. Intermittent water extraction, according to this theoretical explanation of the operability of the present invention, produces his desired effect. Whether or not this theory is correct, it has been firmly established that one of the results of interstage water extraction is the partial removal of water-soluble acids from oxidation ments of total conversions of 10 to 12%, with cooling and water extraction at one-third and two-thirds of the.

total conversion. In a series of such experiments it was found that between the first two stages such water extraction (cyclohexanezwater weight ratio: 10:1) removed 70 to 75% of the acids, 20 to 40% of the esters, 2 to 3% of the cyclohexanone, 4 to 5% of the cyclohexanol and 4% of the peroxy compounds. Both with and without added catalyst, the reoxidation of the water-extracted upper layer gave yields of adipic acid precursors which were about higher than had been realized without water extraction in operations at the same conversion level. The major yield increases were in cyclohexanol and peroxide.

In the previously known processes the decanting of water layer from the condensate produced by the reflux condensers (with which the oxidizers were equipped) also I efiected removal of part of the volatile monobasic acid follows (Table I). The data also show the advantage of interstage water extraction. The temperature in these experiments was 152154 C. The quantity of cobalt naphthenate catalyst was sufficient to produce 1 p. p. m.

cobalt. The rate of air feed was controlled so as to give the desired conversion and an ofi gas containing 0.5%

oxygen.

, i 6 TABLE I Distribution of cyclohexane oxidation products 3-Stage Single Stage Water With Extraction Extracted Reflux Gross conversion, percent 10. 4 9. 5

Yields to:

Cyclohexanone- 31. 0 31. 2 Oyclohexanol..- 36. 0 30. 0 Peroxide 6. 9 3. 7 Adiplc Acid. 6. 5 6. 0

The loss of adipic acid precursors via water extraction of the condensate is surprisingly low, but a surprisingly large part of the monobasic acids is removed in this operation. This fact was proven by carrying out the single stage process by removing from the system all of this condensate, and continuously returning to the oxidation mixture a quantity of cyclohexane equal to that in the condensate. The decanter was operated in the con ventional manner, and the quantities of various products withdrawn as aqueous phase from the decanter were measured. The results were as follows:

TABLE II Oxidation products withdrawn from the oxidation system via the aqueous phase produced in the decanter The data presented in Table II provide a partial explanation as to the value of the water removal-decantation step, which does not very seriously produce losses of adipic acid precursors, but does efiect partial removal of formic and acetic acids from the condensate. The present invention is directed to removing additional amounts of these by-products, which when present in excessive amounts have an undesirable directing effect on the course of the oxidation reaction.

The invention is illustrated further by means of the following example.

Example.Cyclohexane was oxidized with air in the liquid phase under the reaction conditions set forth in Table III (first stage). The oxidation vessel was equipped with a reflux condenser and a decanter for removal of water as fast as formed by the oxidation reaction. After this first stage, the mixture was cooled to room temperature and was extracted with about one tenth of its volume of water, the latter including the water which separated from the decanter. The analyses given show the amounts of products obtainable from the aque ous and hydrocarbon phases. These products, however, were not separated as such, since the mixture of oxidized products ultimately obtained by removal of cyclohexane and water from the final products by distillation, was suitable for use in the nitric acid oxidation process for making adipic acid. As shown in the table, the upper layer from the first stage was used as oxidizer feed for the second stage and the upper layer similarly obtained in the"-second-stagewasus'ed 'as' oxidiz'effeed for the "third"stage." "The'proportions of products form'ed are shown in Table III. For purposes of comparison similar .runswere made without interstage water extraction. The

results are tabulated in Table IV.

. TABLE III "'able by the process of this invention at conversions j higher-than could be used heretofore in obtaining such *Interstage waterextraction in liquid phase bx'idatz'on of cyclohexane .wThelconver-sion togadipic acid precursors obtained in the foregoing example is" shown graphically in Figure 2 of the appended drawings. The curvestshow that interstage waterIextraction-:virtually=eliminates the adverse ef-' a feat of increase'dpercentage conversion ionw-yield of adipic 7 acid p'recursoisel-i Similaroverall results are-obtained by using side-stream extractioninplaceof the multi-stage ex- 1 tractionprocess.

.... .In-- figure curves A;and .C;represent. the results ob "stained as described .in the fdrgoingexample.l...Curve B "esultsobtainedby the previously. described iinilar:conditions whereinphowever, the

"Tcycloh'exa'nefrom the refluxcondensers on eachio'f three First Stage "Second Stage Third Stage Upper layer Upper layer Feed Cyclohexane from first from-second stage stage Catalyst Co (asnaph none added none added 0 r t l t v I i'ithenate) 1 I i onc.o ca ays v p. p. n. ca. vp. .m. ca. .m. "Temperature, O- 154 154 54 Pressure, pas. i. g Lv 132 L .132 132 7 Liquid Residence Time (Min.).- 14.8 a 14. 7 14.9

Air/Feed Ratio (thousands of cubic feet, P 1 standard conditions/gali-per min.);.... 0.35 0.35 0.35 Oz in Off Gas, M01 Percent 0. 9 0. 7 0. 7

. Net Gross Net 'Gross Conversion, Percent.- 3. 82 5.63 7. 33 3. 18 Percent Yield to:

Cyclohexanone 23. 4 27. 2 25. 2 44. 8 Cyclohexanol- 40.5 41.3 40.9 24.6 T Peroxidewal peroxide)- 1 10.3 .2 8.8 2.4 U Adipic Acid" 6.1 5.5 5.8 8.3 "Carbon Oxides" 1.9 2.7 2.3 3.7

Qther Acids 7.0 8.1 5.4 8.9 Sum -of Cyplohexanone, Oyclohexanol,

: Ad1pic Acid, and Peroxide 80. 3 81. 2 80. 7- 80. 1

"TABLE IV high yields. ..The.qadipic-acid precursors include-those Single step oxidations paralleling thoseof Tam/ 1H which are specifically hereinabove mentioned aswell as 7 (no intersmge extraction) lactones, cyclohexyl esters, and other products formed in 40 relatively minute quantity. Under certain conditions the I 2 3 relative amounts ofthese precursors can be varied but i such minor variations do not interfere'with the beneficial moyclo' results which are achieved by the process of this invenhexane hexane hexane i Feed Catalyst Go (as 00 (as Co (as F V P naphthe- P The extraction'step can becarrred out at anysuitable nate) hate) nate) temperature; Runs carried out with extractions atroom a e 1 pm; ppm temperature, 70 and 140 C. (under pressure) gave i i emperature. 9 1577-153 153 153-155 substantially thesarne results. ressure p. s. 130 ,130 130 1 4 Liquid fiesid 15 i 15 15 While the water entraction process of this invention 1 50. permits-operation at virtually constant yield Wlfll increas- 0 7o 1 05 w ing conversion as'hereinabove exp1ained, it is noteworthy 0. 9 0.7 0.7 that control'ofv acid concentration in theoxidation mixture ,gggggg eg g gq 6 1L4 by means of aqueous sodium hydroxide is not-an effective -Cyclohexa.none ,255.5 29. 2 3 29. 2 method forv increasing yield. =The acid level in the oxidizer g$fi% fg '5flg; f is act ually increased-instead of decreased by-addition of g in 'o icggxl j 1 3 -CaUSt1c. ThlS henomenon has been repeatedly observed. ti o dg 'jj" 3:219 A related phenomenon has been observed when mono -0th'er Acids -6.1 7.0 s 8.0 Sum oyclohexanone, cyclm 1 basic acids are introduced into the oxidation mixture in e. p c tentionally up to the amount normally produced. When 3Z9 thi i done, the formation of additional monobasic acid is suppressed. In fact, it has been observed that there is a perceptible improvement in overall yield when a'small "amount (2%) of'monobasi'c' acid is'added." Thewater "extraction process-thus holds the monobasic'acid content at a low optimnm levelfi Complete removal by caustic is -thus not advantageous; when compared with iwater w extraction; but is in :c'ertairr respects disadvantageous. :Periodic:waterextraetion lowers the acid conteiitto a 1evel which is suitable forcontinued high yield-operation. .It is to beunderstoodnliat the ..above examples are illustrative only and that many waysof. practicingthe inventiori..will occur to those who are skilled in the art. For example, the process can be operated in an intermit- -""rii'iidizers in series is returned to the first ox dizer 'rathei" tent or batchwise manner, but, of course, the advantages of the invention are of the greatest value when the process is operated continuously.

Since many difierent embodiments of the invention are readily apparent, it will be understood that we do not limit ourselves except as set forth in the following claims.

We claim:

1. A process for manufacturing partial oxidation products of cyclohexane, including cyclohexanol and cyclohexanone, which comprises reacting cyclohexane in the liquid phase with gaseous oxygen at a temperature of 75 to 200 C. under a pressure of 50 to 500 pounds per square inch in the presence of a hydrocarbon-soluble compound of cobalt as oxidation catalyst, at least part of the oxidation mixture being extracted with water prior to completing the said partial oxidation, continuing the oxidation while separating water from the oxidation mixture substantially as rapidly as the said water is formed by the oxidation reaction, until the overall percentage of cyclohexane which has become oxidized is from 5% to 20%, admixing water with the resulting oxidation mixture, and separating cyclohexane therefrom whereby oxidation products of cyclohexane, capable of further oxidation to adipic acid, are obtained.

2. Process of claim 1 wherein the conversion of cyclohexane is within the range of 10% to 20%.

3. Process of claim 1 wherein the oxidation is conducted in a succession of stages and the extraction with water occurs between stages in the oxidation.

4. Process of claim 1 wherein the extraction with Water is performed on a side stream withdrawn from the oxidation reaction mixture, the extracted organic phase being returned to the oxidizer.

5. Process of claim 1 wherein the said removal of water substantially as rapidly as the said water is formed by the oxidation is accomplished by continuous azeotropic removal of the said water, while the oxidation is in progress.

References Cited in the file of this patent UNITED STATES PATENTS 2,285,914 Drossbach June 9, 1942 2,439,513 Hamblet et a1. Apr. 13, 1948 2,557,281 Hamblet et a1. June 19, 1951 2,565,087 Porter et a1 Aug. 21, 1951 2,703,331 Goldbeck et al. Mar. 1, 1955 

1. A PROCESS FOR MANUFACTURING PARTIAL OXIDATION PRODUCTS OF CYCLOHEXANE, INCLUDING CYCLOHEXANOL AND CYCLOHEXANONE, WHICH COMPRISES REACTING CYCLOHEXANE IN THE LIQUID PHASE WITH GASEOUS OXYGEN AT A TEMPERATURE OF 75* TO 200*C. UNDER A PRESSURE OF 50 TO 500 POUNDS PER SQUARE INCH IN THE PRESENCE OF A HYDROCARBON-SOLUBLE COMPOUND OF COBALT AS OXIDATION CATALYST, AT LEAST PART OF THE OXIDATION MIXTURE BEING EXTRACTED WITH WATER PRIOR TO COMPLETING THE SAID PARTIAL OXIDATION, CONTINUING THE OXIDATION WHILE SEPARATING WATER FROM THE OXIDATION MIXTURE SUBSTANTIALLY AS RAPIDLY AS THE SAID WATER IS FORMED BY THE OXIDATION REACTION, UNTIL THE OVERALL PERCENTAGE OF CYCLOHEXANE WHICH HAS BECOME OXIDIZED IS FROM 5% TO 20%, ADMIXING WATER WITH THE RESULTING OXIDATION MIXTURE AND SEPARATING CYCLOHEXANE, THEREFROM WHEREBY OXIDATION PRODUCTS OF CYCLOHEXANE, CAPABLE OF FURTHER OXIDATION TO ADIPIC ACID, ARE OBTAINED. 